It is known to subject large buildings, such as commercial office buildings or high rise hotel, apartment or condominium buildings, to positive air pressure relative to outside atmospheric pressure. An important reason for such pressurization is to reduce or eliminate air infiltration into a building through open or leaking doors or windows or otherwise through the building's exterior envelope. Such infiltering air, which bypasses the building's heating, ventilation and air conditioning or air handling (“HVAC”) systems, can lead to indoor air quality problems, arising from undesirable contaminants and moisture carried by the infiltering air. Uncontrolled moisture in particular can be problematic, for example leading to damage of building components or to development of mold or mildew. Positive pressurization of the building reduces such problems.
Typically, to establish and maintain a positive pressure inside the building, air is blown by a fan into central interior portions of the building, thereby creating a high pressure zone relative to outside atmospheric pressure. As a result, an air pressure gradient is established across the building from the central portions of the building across the building envelope to the exterior. Air will tend to flow from zones of higher pressure to zones of lower pressure, following the gradient and at a rate dependent on the tightness of the building envelope, of In a typical office or high rise residential building, such as an apartment or a condominium building, the higher pressure air is introduced into the common areas (e.g. hallways, corridors, elevator lobbies) which are typically located in the central core area of the building. The individual office or residential units or suites are usually clustered around the central core so as to afford each unit access to, or views of; the exterior.
The individual units are separated from the common areas and from each other by walls made (for obvious security, safety e.g. fire and smoke, noise, privacy and other reasons) of highly robust materials. For example, such walls may be made of concrete blocks, concrete panels or poured concrete. In most cases, such walls will be finished on both sides, for example by paint or by rigid sheet materials (e.g. taped and painted drywall or gypsum board). Typically, such wall structures comprise air flow barriers which are highly resistant or essentially impermeable to the flow of air therethrough.
Other common building materials which, if joints and seams are sealed, may also act as air barriers in a wall include sheathing materials such as plywood or oriented strand board (OSB), supported flexible barriers (e.g. polyethylene sheets), properly applied specialty air barrier compositions, rigid sheet insulation, glass blocks, sheets of glass and unperforated housewraps.
Some building materials, while resisting airflow therethrough, may nevertheless allow some air to pass. Examples may include some housewraps, felt papers and spray cellulose. Such materials may be known as air flow retarders.
Access from the common areas to the individual units is achieved through doorways in the wall. Door frames (consisting of two side jambs, a head jamb and possibly a sill or threshold) are installed in the doorway openings. Again, for security and other reasons, the door frames are typically made of highly robust materials, such as steel, and are solidly mounted to the wall.
The doors, mounted on hinges to the door frames, are also of made of highly robust materials, such as steel or heavy wood panels and possibly with cores of insulation. Such door paneling materials also typically are air flow barriers.
In buildings with the above structures, the pressurized air in the common areas, being unable to flow through the walls into the individual units, can only flow through the doorways. When the doors are closed, which typically would be most of the time, the air may only flow into the units around the edges of the doors, namely between the side edges of the door and the side jambs of the door frame, between the upper edge of the door and the head jamb of the door frame and between the lower edge of the door and the sill or threshold (if there is one) of the door frame or the floor itself (if there is no sill or threshold).
Although the structures described above are adequate to prevent or reduce problems of infiltration into the building of untreated outside air, they do not in any way address, let alone solve, problems associated with the flow of air along the pressure gradient from one zone of the building to another. In particular, they do not address the problems associated with air flow from the common areas into the individual units.
For example, regardless of the fact that dirt and other contaminants may not be brought into the building by means of air infiltration, dirt and other contaminants are nevertheless present due to generation within the building or being brought into the building by various means. For example, residual dust and dirt may be present from the original building construction. In addition, dust and dirt will be brought into the building by people entering the building or may enter the building through open doors and windows. Dust and dirt may also be generated during building repairs or the innumerable activities of people inside the building. In addition, people and their pets are organic beings which constantly shed biological materials, such as dried skin and hair. All of these and other contaminants may be present in the form of airborne dust or other heavier particulates capable of being moved by flowing air.
Especially because the common areas of the building will typically have more traffic than individual units, a significant amount of dust and dirt can be present in the common areas. Some of that dust and dirt is entrained in the air in the common areas which then flows from the common areas into the units, as described above.
In this manner, contaminants are moved from one zone of the building to another by means of the air flow described above. The air flow beneath a door in many cases is quite considerable particularly if the gap is not interrupted by a threshold beneath the door.
There is thus a need for a structure which will reduce or eliminate the movement of dirt, dust and other contaminants from a pressurized zone of a building into an adjacent zone of the building.